NEMO-Chemistry
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Calcium Carbonate and HCL
Sorry for the stupid nature of the question, but its kind of bugging me.
As Calcium Chloride is useful and mostly i wouldnt need pure stuff, I decided go to the beach grab some shells and dissolve in HCl until PH reached
neutral.
I have done a small test just to make sure, and something unexpected happened.
500ml Conical flask, 100ml 36% HCl (reasonable grade)
270ml plain water from tap (it was just a test)
I started putting shells in and loads of CO2 evolved, i didnt bother weighing the shells i just wanted an idea of what to expect when on a larger
scale and what kind of product i would get.
First few shells completely dissolved, leaving some organic bits from the shells on the bottom of flask.
I figure these could be filtered later. The reaction was rapid and loads of foam, i kept on adding a few shells at a time and with universal paper the
PH was around 1.
The PH paper is cheapo Chinese BTW.
As i continued adding shells the liquid started to turn dirty in colour (expected as shells not cleaned) but a fine pure white powder starting to fall
out of the solution.
My guess was the solution becoming saturated with calcium Chloride and the powder falling out. At this point i was pleased and just assumed i could
redissolve when finished and filter, then boil down and recover the product.
Eventually the white layer with some crud built up and the reaction slowed, the PH showed 2 on the paper.
Now the bit i didnt expect......
Eventually no more shells were dissolving, a few tiny bubbles of Gas off them but several days and the shells still there.
So I test PH and its still roughly 2, I thought maybe more water was needed so put everything into a 1 LTR flask and added around 200ml more water.
NOTHING! no more reaction. So i check calcium Chloride on wikipedia for the PH and it says between 6.5 and 8 depending on Anhydrous etc.
According to my paper its still around 2. So i am a bit lost here, why are the shells no longer dissolving? Is it likely its just crap paper?
Has the solution become so saturated with a drying agent it takes all the water needed to help the reaction?
I am considering decanting the solution and boiling down, collect the product, wash and redissolve then boil down again and collect.
With the solid thats in the bottom already i thought i would dissolve filter and boil as above.
But the PH worries me, surely it should almost reach 7 before no more reaction?
Anyone got any ideas what has happened and what idiot mistake i have made.
I am more than happy to weigh the shells and repeat but i figured little point as no way to really know the amount of calcium carbonate in them.
Thanks in advance, i am sure its just me not understanding what happens more than anything else, or maybe PH paper thats not very good.
It does show a PH roughly around 6-7 for the tap water which would be about right around here.
I have done a smaller scale as well with same results, if needed i can post the pics and show the paper colour as well.
[Edited on 27-7-2016 by NEMO-Chemistry]
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MrHomeScientist
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It's likely the calcium chloride isn't very soluble in hydrochloric acid solution - I've had a similar experience with table salt dropping out of
concentrated acid. I'm surprised diluting it didn't work. Maybe try neutralizing a little of the acid directly with a hydroxide and see what that
does.
And being a "drying agent" has no effect whatsoever when in solution. It has to be a solid, and even then it has to be heated enough to drive off the
water in its original dihydrate form. And even if all that is true and you do have dehydrated calcium chloride, it is only capable of absorbing trace
amounts of water. You can't suck all the water out of a beaker by dropping in a drying agent.
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NEMO-Chemistry
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Quote: Originally posted by MrHomeScientist  | It's likely the calcium chloride isn't very soluble in hydrochloric acid solution - I've had a similar experience with table salt dropping out of
concentrated acid. I'm surprised diluting it didn't work. Maybe try neutralizing a little of the acid directly with a hydroxide and see what that
does.
And being a "drying agent" has no effect whatsoever when in solution. It has to be a solid, and even then it has to be heated enough to drive off the
water in its original dihydrate form. And even if all that is true and you do have dehydrated calcium chloride, it is only capable of absorbing trace
amounts of water. You can't suck all the water out of a beaker by dropping in a drying agent. |
Interesting thanks, maybe i havnt added enough water then. I have some sodium hydroxide but might try and get some calcium so i can use that instead.
Acids are pretty interesting, especially when they dont do what you expect!
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MrHomeScientist
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Calcium hydroxide takes some effort to dissolve and react - I'd prefer one of the alkali hydroxides personally, as long as minor cation contamination
isn't an issue. You could always re-precipitate with carbonate (the sodium stays in solution) and repeat the acid dissolution to get pure
CaCl<sub>2</sub>.
I definitely appreciate wanting to make your own reagents, especially from such common materials as sea shells. But if you need a lot of it as a
desiccant, they do sell it in a product called Damp Rid. Just something to think about for the future. Keep on experimenting!
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NEMO-Chemistry
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| Quote: Originally posted by MrHomeScientist | Calcium hydroxide takes some effort to dissolve and react - I'd prefer one of the alkali hydroxides personally, as long as minor cation contamination
isn't an issue. You could always re-precipitate with carbonate (the sodium stays in solution) and repeat the acid dissolution to get pure
CaCl<sub>2</sub>.
I definitely appreciate wanting to make your own reagents, especially from such common materials as sea shells. But if you need a lot of it as a
desiccant, they do sell it in a product called Damp Rid. Just something to think about for the future. Keep on experimenting! |
I will try a little with sodium hydroxide and see what happens.
My interest is actually trying to get reagents as pure as i can from things i find etc. Almost like old Alchemy in way.
I did put 10ml of the solution in 2M solution of Sulphuric acid and calcium sulphate pure white drop out of the solution.
Being a sulphate and very insoluble i want to wash this and the make nitrate with nitric acid.
Sure it's probably got a little magnesium and sodium in from the shells but this dosnt worry me for general use.
The shells are a mix of types, but i found that Oyster shells seem to be far more calcium than most types (from reading and the way they are).
I can buy reagents as i go along but there is alot of satisfaction from making them  .
I have pure (99.9%) calcium carbonate i got from school, i will try this as well. I have a fair bit of conc HCl, but i would like to try and make some
from Chlorine and Hydrogen.
I am also making the bits i need for a chlorate/perchlorate cell. I dont need or want much but i do like the idea of making some.
I especially want to make the anode myself from lead nitrate, although getting enough lead proved pretty hard around here!
No idea what i am going to do it i want to make anything with mercury!!
I also like the idea of making several reagents from a single starting point.
I have ordered some aspirin, originaly the idea was just to make copper asprinate (sorry i know thats the wrong term), then i got to thinking what
others i could make.
So i would like to try manganese and maybe a couple of others, then there is oil of wintergreen as well. I dont intend making huge amounts but its
kind of like element collecting but compounds instead .
So copper nitrate,chloride,sulphate,asprinate ect all starting from copper wire.
My experimenting is outdoing my reading at the moment, so i should read more so i understand things better. But you cant beat watching things happens!
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Deathunter88
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I remember when I just started doing chemistry experiments I had the same confusion as you. When making salts I was always trying to get to a neutral
point but the pH always stayed lower. I realised with time that its very difficult to achieve theoretical neutralisation in the lab (when preparing
salts). However, by the time the pH of a strong acid solution is around 2, it is of relatively low concentration. So instead of killing yourself over
it, just filter and boil down the solution.
PS. It is completely normal to have carbonate sitting on the bottom of a beaker of still acidic solution since the reaction is so slow. Don't worry,
just filter and boil.
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NEMO-Chemistry
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| Quote: Originally posted by Deathunter88 | I remember when I just started doing chemistry experiments I had the same confusion as you. When making salts I was always trying to get to a neutral
point but the pH always stayed lower. I realised with time that its very difficult to achieve theoretical neutralisation in the lab (when preparing
salts). However, by the time the pH of a strong acid solution is around 2, it is of relatively low concentration. So instead of killing yourself over
it, just filter and boil down the solution.
PS. It is completely normal to have carbonate sitting on the bottom of a beaker of still acidic solution since the reaction is so slow. Don't worry,
just filter and boil. |
Thanks for the info!
To me PH2 is really acidic so i assumed it would get to around 5 or 6, good to know that what i am seeing is normal.
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NEMO-Chemistry
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Now that was interesting and NOT what i expected! I put around 1/4 teaspoon maybe slightly less of sodium hydroxide micro prils in a flask.
I then added around 35ml of the sodium chloride/acid solution to it. I was expecting Gas and froth and some heat, instead i got an instant milk
coloured very fine precipitate and couldnt see any gas evolve and there was little if any heat.
So iassume the solution isnt as acidic as i was expecting. Also i moved one the shells and a bubble of gas was trapped underneath, so i guess its
still very very slowly reacting.
I will do a much larger scale version and see what happens, but appears that everything is ok. Maybe the jump from PH2 to neutral when it happens is
pretty fast.
No idea at this point but as it seems to be fairly normal i am not worried and i will leave the larger batch (2 ltr acid and 4 ltr water) for a couple
of weeks with whole shells in.
I figure once its reached the point this scale has i can remove any large lumps of shells left, that way i get minimal calcium carbonate in it, not
that it matters seeing as it will be turned into sulphate and nitrate etc.
Thanks for the help and info, its made it much more interesting.
I take it the milk colour is mostly calcium hydroxide? pretty neat the way it went pure white and just like milk as soon as the solution was added to
the flask with prills in.
The sodium hydroxide is supposed to be fairly good grade and the prils are very small (more like small crystals).
I have some sodium carbonate (dubious grade) and sodium hydrogen carbonate (pretty pure 99%), so i might titrate the acid/chloride solution and get a
rough idea what the strength actually is of the acid thats left.
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DraconicAcid
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Why would you expect gas and froth when adding an acidic solution of calcium chloride to sodium hydroxide? Your precipitate will be calcium
hydroxide, probably with a bit of calcium carbonate (since it's very difficult to keep sodium hydroxide carbonate-free unless you're working in a
glove box).
Please remember: "Filtrate" is not a verb.
Write up your lab reports the way your instructor wants them, not the way your ex-instructor wants them.
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NEMO-Chemistry
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| Quote: Originally posted by DraconicAcid | | Why would you expect gas and froth when adding an acidic solution of calcium chloride to sodium hydroxide? Your precipitate will be calcium
hydroxide, probably with a bit of calcium carbonate (since it's very difficult to keep sodium hydroxide carbonate-free unless you're working in a
glove box). |
Because the PH was 2 and i started with Hydrochloric acid, i was unsure how much if any acid was there.
I expected froth and brimstone after adding a small amount of acid to hydroxide months ago. It was conc sulphuric and not much hydroxide but it
reacted with a fair bit of vigour to say the least.
I guess that experience made me think anything acidic with sodium hydroxide would be impressive, especially as when i first added the shells to the
hydrochloric it fizzed like crazy.
Its all a learning curve but great fun.
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NEMO-Chemistry
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I wont describe everything i have done as this will.
A. Sound very stupid.
B. Complicate things
So just to double make sure with this......
I added pretty much saturated Calcium Chloride to a tiny amount of Sodium Hydroxide (no way for me to measure that amount), I did this by adding maybe
4-5 tiny crystals/prils of Sodium hydroxide to a large test tube and then Adding the saturated solution of calcium Chloride.
I got a ultra fine white participate which is likely to be Calcium Hydroxide and a solution of Sodium chloride?
I decided to have another with this as the Calcium Chloride solution was around PH2, i wondered if by adding Sodium Hydroxide i could neutralise the
solution to around the correct value, I didnt get as far as measuring because i got side tracked.
I wondered what would happen if adding a strong solution of Sodium Hydroxide to a saturated solution of Calcium Chloride solution. I didnt weight the
Sodium Hydroxide as this was test tube scale and didnt need to be exact.
I filled the bottom of a large test tube with 4-6mm layer of Hydroxide prils and added around 50ml of water to it. The solution of sodium Hydroxide
went cloudy and got hot before cooling down and clearing.
I added the solution of Sodium Hydroxide to the Calcium Chloride, this time instead of a ultra fine suspension of white solid i got an instant
slightly thicker suspension with particles sizes a big bigger than before.
The best way to describe this is upon adding the solutions together you get a thick tangled layer that looks alot like a cloud of white, shake it all
up and you get a slightly thicker white suspension of larger particles than when i used the very dilute Hydroxide solution.
Now normally the sensible thing to do is stop there. Try and separate the products etc etc.
But sensible isnt me. Because of the battery gunk thing and because i have been reading of permanganate's, i wondered what would happen if i added a
couple of crystals of Potassium Permanganate.
I know of the clock experiment and i know adding water sugar etc you get several colour changes over time.
But i also know Permanganate reacts with both chloride and Hydroxide, so what about when both are together.
I added a couple tiny crystals to the tube with the white suspension that had started to settle.
Bright red colour, then it started to darken until a really nice purple, from there i got a darker purple/mauve then it started to change to hues of
Purple almost blue. Eventually turning a dull grey and at that point i had to stop.
Now kind of impossible for me to know what happened as i had too many unknown ions around in unknown quantities.
I also noticed a small amount of gas being evolved, this had no smell and was colourless. Next step now i know if i add a stronger sodium hydroxide
solution to the calcium chloride, i get something with particles that are large enough for me to filter.
So Next is to Add Permanganate to each separately and see what happens and what colours i get, i will see if i can get enough gas so i can test it. If
i am starting to understand what i read then my gas should be Oxygen.
I am also going to try dissolving the shells in Sodium hydroxide first, this should give me Calcium Hydroxide and sodium Carbonate?
I am at this point just trying to find the best way to clean up the material from the shells so they can be used to make reagents. I originaly chose
chloride and still think this might be best route.
But the hydroxide gives me something easy to filter and wash. No harm in keep experimenting and then go from there.
No real question i just thought i would post what i was upto.
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NEMO-Chemistry
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Not explained any of the above well! I am working out how to do the equations, then i will come back and explain as clearly as i can with pics what i
am doing!!
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